An organic EL (electroluminescence) device, a typical example of an organic semiconductor device, is a light emitting element which utilizes a luminous phenomenon during recombination of electrons and holes in an organic semiconductor layer. More specifically, the organic EL device comprises an organic semiconductor light emitting layer, an electron injecting electrode for injecting electrons to the organic semiconductor light emitting layer, and a hole injecting electrode for injecting holes to the organic semiconductor light emitting layer (refer to Japanese Unexamined Patent Publication No. 05-315078 (1993)).
To improve the light emitting efficiency, the number of carriers (electrons and holes) to be injected in the organic semiconductor layer must be appropriately balanced. To that end, the combination of respective materials of the organic semiconductor layer, the hole injecting electrodes, and the electron injecting electrodes must be properly selected, and further, the hole injecting electrodes and the electron injecting electrodes must be positioned properly. In practice, however, the proper selection of the materials still remains difficult.
Alternatively, organic semiconductor layers may be used as a photosensitive layer to configure an optical sensor. The photosensitive layer has the function of photoelectric conversion, which generates pairs of electrons and holes through external light irradiation. In this case, too, in order to gain desired sensitivity, combination of respective materials of the organic semiconductor layer and the pair of electrodes must be properly selected and their location must be appropriately arranged. However, it is difficult to design a configuration of desired characteristics.
Further, in the cases mentioned above, neither the device that emits light nor the device that detects light can change the light emitting/receiving characteristics. Devices should thus be individually designed for specific applications.